1. Technical Field
The present invention relates to a nacelle and wing assembly of an aircraft, and more particularly to such an assembly with means to improve aeordynamic performance when operating at high angles of attack where there is interaction of nacelle wake and wing boundary layer at near stall condition.
2. Background Art
It is quite common in present day aircraft designs to place the engine nacelle below the wing with the inlet of the nacelle being positioned forwardly of the leading edge of the wing. This nacelle/wing assembly is normally designed so that in cruise configuration the air flow around the nacelle causes relatively little disturbance to the airflow adjacent the wing. However, landing and/or take off performance is tied to the stall speeds at various flaps down configurations. The higher the stalling angle of attack, the lower the stall speed and hence lower takeoff and landing speeds, resulting in shorter field length. At these high angles of attack, corresponding to stalling of high lift configurations, the nacelle sees an even higher angle due to the wing lift induced upwash. In many wing nacelle assembly configurations, the effect is an undesirable interaction of the nacelle and wing flow fields which reduces the lift which might otherwise be achieved.
One prior art approach to identify the nature of the problem and provide an appropriate solution is disclosed in U.S. Pat. No. 3,744,745, Kerker et al, where there is shown a nacelle/wing assembly, with a swept back wing and an engine nacelle mounted downwardly and forwardly of the wing leading edge. Mounted on the forward upper surface portion of the engine nacelle just behind the nacelle inlet are a pair of lift vanes. The text of the patent indicates that these vanes produce a downwash field between trailing vortices in the vicinity of the wing leading edge. It is further alleged that this field in turn reduces the high suction pressure peaks on the wing leading edge aft of the engine nacelle, tending, in turn, to delay the onset of airflow separation at the wing trailing edge forward of the flap. It is further stated that this delay in airflow separation permits the wing to generate more lift.
While it is generally known that vanes can be used to improve performance of nacelle/wing assemblies in a high lift mode of operation, these same vanes have an undesirable aspect in that for cruise mode of operation, they will normally tend to increase drag. Therefore, in general, it is desirable to size these vanes to alleviate the drag problem for cruise configuration, and yet to arrange the configuration and location of such devices to optimize their desirable effects in improving performance during the high lift/high angle of attack mode of operation.
However, the task of designing devices to modify the airflow about a nacelle wing assembly is enormously complex. In the design of an aircraft, generally the overall configuration of the wing and nacelle are at a certain stage of the design fixed within certain limits. If an aerodynamicist had the luxury of unlimited time to test a particular nacelle wing assembly in the wind tunnel, with unlimited budget, then he could embark on an extended experimental program of placing flow modifying devices of various configurations at various locations and eventually, by a lengthy process of trial and error, the overall design could be optimized. However, as a practical matter, where the entire airplane must be designed within certain budget limitations, such endless experimentation is not possible. Therefore, it becomes incumbent upon the aerodynamicist to analyze the performance and flow patterns of a given nacelle/wing assembly to determine which experimental avenues might be examined more advantageously to optimize performance. To conduct this analysis successfully with reasonable consistency requires not only an understanding of the aerodynamic phenomena which exists for a particular nacelle/wing assembly, but also what sort of flow modifying means might be employed successfully to be effective in resolving the problems associated with that particular phenomena.
In view of the foregoing, it is an object of the present invention to provide a nacelle/wing assembly with appropriate wake control means, a method of designing and building such an assembly, and a method of utilizing such an assembly, where, with the wing nacelle assembly in a high lift, high angle of attack mode of operation, certain aerodynamic phenomena exist which are alleviated by effective use of certain wake control means.